Once I got the spring where I wanted it in relation to the blade. I made sure I was pressing up snug and applied the super thin super glue to hold the spring in place for drilling. After screwing up two sets of liners doing these knives I changed my method.
Old method
1 fit spring and super glue in place on rough liners
2. drill end pin
3. remove spring with tap from mallet.
4. clean area with acetone
5. mark spot for middle pin
When using the thin super glue I would either use too much and glue the blade, bushing, pivot pin, spring, and liners all together in one big mess. It was a hassle and if I used too much while drilling the spring my pop loose and I would end up drilling the hole just a hair off.
Now I use parallel clamps
I clamped the blade in place first, then clamped in the middle of the spring. This left the end pin open for drilling.
I had to do some manuevering and re zeroing of my drill press to let the screws from the clamps hang down but I got it done.
Now with the pivot pin and the end pin drilled I had to worry about the middle pin. The middle pin is the pin I drill offset to load the spring. I've read and talked to other makers about how they do their loading and I have gotten different answers. Some makers do it off the pivot pin, some off the middle, and some off the end pin.
I also don't have a good forumula of how much to load the spring. Like I've said before I've only made a hand full of slip joints and they have all been a litte different, but I'll show you what I've done on these knives.
With the blade and spring in place on the liners with pins in the drilled holes and the blade in open position I use an exacto blade to mark a line on the back side of the spring. I made sure I was right up against the spring because I was going to measure off of this line.
I could't get it to show up well so I highlighted it with a marker
From here I left the end pin and removed the blade. Next in the pivot area of the blade I measure up 1.5mm from the scribed line. I then clame the spring down in this position. The spring is 1.5mm from where it used to set on one end and closer to the middle pin it is less than that. I think the Tony Bose tutorial is 1/3 of the hole. Once I got the spring where I wanted it I clamped it down.
I then drilled the 3/32" middle pin hole.